Bull is the largest summon in Kakashi's ninken pack. He has dark fur and wears a spiked collar. He also wears the standard outfit of Kakashi's ninken which consists of a blue vest with the heno-heno-moheji seal and a Konoha forehead protector worn on his left front leg.
Befitting of his name, he is a large, intimidating black bulldog wearing a spiked collar. Unlike all the other members of Kakashi's ninken pack, Bull does not appear to have the ability to speak. Nonetheless, he and Pakkun seem to get along well enough for him to allow the latter to ride atop his head. Comparatively, Bull is the largest of Kakashi's ninken.
Bull possesses heightened senses with which he can use to track his target with ease. He has also demonstrated the ability to track his target underground through the use of the Summoning: Earth Release: Tracking Fang Technique as well as hold a target down, allowing Kakashi to attack them freely. He also has has exceptional teamwork with the rest of his pack, able to develop and effectively use several offensive and defensive formations in battle which make use of the manoeuvrability and powerful limbs.
You can download this cube Naruto paper craft model from here: Naruto - Big Bark Bull Cube Craft Free Paper Toy Download